Thousands of households face a rise in the cost of energy next month as popular fixed rate tariffs from the major suppliers come to an end.

Bill payers face being moved back on to their supplier's standard tariffs, which are often substanitally more expensive.

Price comparison website MoneySuperMarket.com estimates the rise could be up to £280 on an annual bill.

Four of the "Big Six" energy suppliers - E.ON, npower, Scottish Power and EDF Enregy - are due to end some of their tariffs.

Lucy Darch, head of energy at MoneySupermarket.com, said: "There are a number of fixed rate energy deals coming to an end over the next month and with rumours abound of imminent price rises, now is the time to act before you see your bills rocket.

"Most people will be moved on to their provider's standard price plan unless they take action so in order to avoid a bill shock it's well worth taking five minutes to find a new deal."

However, the fixed deals on offer will not be as low as the ones customers took last year. Ms Darch added: "There are a number of fixed rate products available to customers over the short and long term with savings up to £204 to be made by switching."

Energy suppliers are obliged to inform fixed deal customers 30 days before a tariff is about to end but it takes approximately six weeks to switch. "It is best to strike first and start the process early," said Ms Darch. "If you haven't received a notification from your provider yet but think your tariff ends soon, contact them immediately to find out the date your current deal expires."

Other ways to save money on energy bills include taking dual fuel - gas and electricity from the same supplier - or paying by direct debit. The best way to compare tariffs and calculate the saving is to use a comparison service. The Telegraph offers a comparison service via the button below.

Those who choose variable tariffs over fixed rate tariffs can also save more - as variable deals are priced more competitively, but of course they do not come with the benefit of fixed price peace of mind.

Below are the big six energy suppliers and the price rises in their standard rates since they last changed their tariffs in Autumn/Winter 2012. The change in their tariffs over the coming months are likely to follow similar price hikes.

Supplier

Gas

Electricity

Date

British Gas

6.4%

6.6%

16-Nov-12

EDF Energy

10.8%

10.8%

07-Dec-12

e.on

9.4%

7.7%

18-Jan-13

npower

8.8%

9.1%

26-Nov-12

SSE

9.3%

10.2%

15-Oct-12

Scottish Power

8.5%

9.0%

03-Dec-12

Average

8.9%

8.9%

Source: energyhelpline.com. Rates correct as of 02.08.13

The best fixed energy deal on the current market is M&S's Fix & Save, which costs a medium energy user paying by direct debit an average £1,139 - but charges a hefty £50 cancellation fee.